Our knowledge of regulatory mechanisms in mycoplasmas is negligible, apart from scattered information on enzyme induction in a few Mycoplasma species. The long-range goal of the proposed research is to seek out the regulatory phenomena associated with ATP generation in Mycoplasma arthritidis. Nonglycolytic mycoplasmas can be adapted to grow on arginine as a single energy source. The sequence of enzymic reactions leading to ATP generation is well known. Some unresolved questions include: is synthesis of arginine deiminase under both positive and negative control (induction and repression) and is its synthesis coordinated with the synthesis of ornithine carbamoyltransferase and carbamate kinase, the other two enzymes in the pathway; what is the subunit architecture of the last two enzymes; and is arginine or one of its metabolites the inducer of the last two enzymes.